At present, there are generally two kinds of techniques for manufacturing heat exchangers, one of which is a mechanical tube expansion technique, and the other of which is a brazing technique.
A common tube-fin type heat exchanger 10 is as shown in FIGS. 1-3. The tube-fin type heat exchanger 10 comprises a plurality of fins 1, each of the plurality of fins 1 being provided with fin holes 2; a plurality of heat exchange tubes 3, each of the plurality of heat exchange tubes 3 passing through corresponding fin holes so as to stack the plurality of fins together on top of one another; at least one bend 4, each of the at least one bends 4 being configured to communicate with two corresponding heat exchange tubes of the plurality of heat exchange tubes 3; and at least one collecting pipe 5 configured to distribute a fluid into the corresponding heat exchange tube 3, and to finally lead the fluid out of the tube-fin type heat exchanger 10. Specifically, a refrigerant passes through the heat exchange tubes, while a medium, such as air, passes through the fins.
As shown in the figures, in general, the heat exchange tubes 3 are circular, and the fin holes 2 are circular as well. With the diameter of the fin holes 2 being slightly greater than that of the heat exchange tubes 3, the fins 1 are penetrated by the heat exchange tubes 3, and after the installation of all of the fins, an expanding head 6 of a tube expander protrudes into the heat exchange tubes 3 to carry out tube expanding. The diameter of the expanding head 6 of the tube expander is slightly greater than the diameter of the fin holes 2. After the tube is expanded, it can be ensured that the heat exchange tubes 3 are closely attached to the fins 1.
A micro-channel/parallel-flow heat exchanger 20 is as shown in FIG. 4. The heat exchanger 20 comprises two manifolds 21, a plurality of flat heat exchange tubes 22 extending between the two manifolds 21, and a plurality of fins 23 provided between adjacent heat exchange tubes 22. In addition, an end cover 24 mounted on one end of the manifold 21, a baffle 25 provided in a cavity of the manifold 21, a side plate 26 mounted on one side of the heat exchanger 20, and an inlet/outlet fitting 27 provided on the manifold 21 are also shown.
All the components of the heat exchanger 20 are made of aluminum. After being tightly bundled up as shown in the figure, the flat heat exchange tubes 22 and the fins 23 are sent into a brazing furnace for brazing, such that the fins 23 and the flat heat exchange tubes 22 are welded together after leaving the furnace. The brazing process includes spraying brazing flux, drying, heating, welding, cooling, etc.
However, as is well known, for a given size of heat exchanger, the smaller the hydraulic diameter of the heat exchange tubes, the higher the heat exchange performance and the lower the material costs. However, the mechanical tube expansion technique is greatly affected by the diameter of the heat exchange tubes, and can currently only be applied to heat exchange tubes with a diameter greater than 5 mm.
Moreover, for a conventional heat exchange tube, taking factors such as the cost and heat exchange efficiency into consideration, the wall thickness is generally designed to be very thin, and when the mechanical tube expansion technique is employed, the tube wall is prone to being expanded until same bursts, causing the product to be scrapped.
As for the other soldering technique, it can be used for heat exchangers having heat exchange tubes with a small hydraulic diameter. Micro-channel heat exchangers usually use this technique and have a relatively good heat exchange performance. However, on one hand, problems, such as the complex brazing process, high equipment investment and unstable product quality, greatly limit the market competitiveness of micro-channel heat exchangers. On the other hand, since the products need to undergo high temperature welding, it is impossible to make an anti-corrosion layer or hydrophilic layer on the materials of the fins, leading to a lower anti-corrosion performance and drainage capacity than tube-fin type heat exchangers.